A
cDNA clone oslea3, encoding a group 3 late-embryogenesis abundant (LEA)
protein was isolated from roots of rice seedlings (Oryza sativa L.). The encoded OSLEA3
protein has previously been found to accumulate to higher levels in roots of two
salt-tolerant compared to a
salt-sensitive rice variety in response to
abscisic acid (ABA) [Moons et al., 1995. Plant Physiol. 107, 177-186]. The OSLEA3
protein (Mr 20.5, pI 6.5) characteristically contains ten imperfect 11-mer
amino acid repeats. Exogenous application of ABA and exposure to
salt shock (150 mM NaCl) rapidly induces a de novo, abundant oslea3 transcript accumulation in seedling roots, whereas application of
jasmonic acid (9 microM) does not induce oslea3 expression. The stress-induced oslea3 transcript gradually declined upon prolonged
salt shock, as wilting-induced damage became irreversible. oslea3 expression was compared for the
salt-tolerant variety Pokkali and the
salt-sensitive cultivar Taichung N1. Higher maximal
mRNA levels were found in roots of the tolerant variety, also declining less rapidly upon sustained
salt shock, concomitant with a delayed drop in shoot water content.
DNA blot analysis indicated the existence of a small oslea3 gene family in rice with an equal gene number in both ecotypes. The results suggest that a differential regulation of oslea3 expression is an aspect of the varietal differences in salt stress tolerance.